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9 Apr 2012

Volume 100, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 153701 (2012); http://dx.doi.org/10.1063/1.3700446 (3 pages)

Hsiao-lu D. Lee, Steffen J. Sahl, Matthew D. Lew, and W. E. Moerner
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In-plane interdot carrier transfer in InAs/GaAs quantum dots

J. Bhattacharyya, S. Zybell, S. Winnerl, M. Helm, M. Hopkinson, L. R. Wilson, and H. Schneider

Appl. Phys. Lett. 100, 152101 (2012); http://dx.doi.org/10.1063/1.3701578 (4 pages) | Cited 1 time

Online Publication Date: 9 April 2012

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Using time resolved photoluminescence (PL) quenching measurements, we investigated inplane carrier transfer in InAs/GaAs self-assembled quantum dots (QDs). THz pulses from a free-electron laser tuned to the intersublevel transition energy were used to excite carriers to higher levels causing quenching in the PL. These carriers could either fall back to the lower energy states and recombine or get transferred to adjacent QDs. The relaxation of the carriers was directly reflected in the recovery of the PL signal. Comparing measurements from two samples, we found that the redistribution of carriers into the neighbouring QDs is the dominant mechanism of carrier relaxation. The data were fitted using a rate equation model to estimate the PL recovery time which we attribute to the interdot carrier transfer time.
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78.67.Hc Quantum dots
78.47.D- Time resolved spectroscopy (>1 psec)
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors

Charge trapping induced drain-induced-barrier-lowering in HfO2/TiN p-channel metal-oxide-semiconductor-field-effect-transistors under hot carrier stress

Wen-Hung Lo, Ting-Chang Chang, Jyun-Yu Tsai, Chih-Hao Dai, Ching-En Chen, Szu-Han Ho, Hua-Mao Chen, Osbert Cheng, and Cheng-Tung Huang

Appl. Phys. Lett. 100, 152102 (2012); http://dx.doi.org/10.1063/1.3697644 (4 pages) | Cited 6 times

Online Publication Date: 9 April 2012

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This letter studies the channel hot carrier stress (CHCS) behaviors on high dielectric constant insulator and metal gate HfO2/TiN p-channel metal-oxide-semiconductor field effect transistors. It can be found that the degradation is associated with electron trapping, resulting in Gm decrease and positive Vth shift. However, Vth under saturation region shows an insignificant degradation during stress. To compare that, the CHC-induced electron trapping induced DIBL is proposed to demonstrate the different behavior of Vth between linear and saturation region. The devices with different channel length are used to evidence the trapping-induced DIBL behavior.
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85.30.Tv Field effect devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Jahn-Teller assisted polaronic hole hopping as a charge transport mechanism in CuO nanograins

M. Younas, M. Nadeem, M. Idrees, and M. J. Akhtar

Appl. Phys. Lett. 100, 152103 (2012); http://dx.doi.org/10.1063/1.3702465 (4 pages) | Cited 3 times

Online Publication Date: 10 April 2012

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Impedance spectroscopy has been employed to investigate the dielectric and electric transport phenomena in sol-gel synthesized CuO nanograins. Semiconducting features of the grains and grain boundaries have been endorsed to the thermal activation of the localized charge carriers. On cooling below 303 K, a transition from Jahn-Teller polaron hopping mechanism to the Mott’s variable range hopping mechanism has been observed owing to random potential fluctuations among localized sites. Activation energies for conduction and relaxation processes at grain boundaries provide strong signatures for the involvement of Jahn-Teller adiabatic small polarons as a charge transport mechanism in CuO nanograins.
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81.05.Hd Other semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
72.20.Ee Mobility edges; hopping transport
73.63.-b Electronic transport in nanoscale materials and structures

Embedded-gate graphene transistors for high-mobility detachable flexible nanoelectronics

Jongho Lee, Li Tao, Yufeng Hao, Rodney S. Ruoff, and Deji Akinwande

Appl. Phys. Lett. 100, 152104 (2012); http://dx.doi.org/10.1063/1.3702570 (4 pages) | Cited 8 times

Online Publication Date: 10 April 2012

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A high-mobility graphene field-effect transistor with embedded gate was fabricated on smooth spin-coated polyimide films. Electrostatic transport measurements reveal a maximum electron and hole mobility of 4930 cm2/V s and 1130 cm2/V s, respectively. Temperature dependent measurements indicate that carrier transport is not limited by intrinsic mechanisms but by charged impurities, surface roughness, and defects, suggesting that further increases in mobility are possible. The measured carrier mobilities are the highest reported for graphene transistors on polymeric substrates and hence enable high-speed devices for flexible electronics from graphene grown by size-scalable chemical vapor deposition.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Structural properties of InN films grown on O-face ZnO(000math) by plasma-assisted molecular beam epitaxy

YongJin Cho, Oliver Brandt, Maxim Korytov, Martin Albrecht, Vladimir M. Kaganer, Manfred Ramsteiner, and Henning Riechert

Appl. Phys. Lett. 100, 152105 (2012); http://dx.doi.org/10.1063/1.3702572 (4 pages) | Cited 3 times

Online Publication Date: 10 April 2012

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We study the impact of substrate temperature and layer thickness on the morphological and structural properties of InN films directly grown on O-face ZnO(000math) substrates by plasma-assisted molecular beam epitaxy. With increasing substrate temperature, an interfacial reaction between InN and ZnO takes place that eventually results in the formation of cubic In2O3 and voids. The properties of the InN films, however, are found to be unaffected by this reaction for substrate temperatures less than 550 °C. In fact, both the morphological and the structural quality of InN improve with increasing substrate temperature in the range from 350 to 500 °C. High quality films with low threading dislocation densities are demonstrated.
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81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Coincident site lattice-matched InGaN on (111) spinel substrates

A. G. Norman, P. C. Dippo, H. R. Moutinho, J. Simon, and A. J. Ptak

Appl. Phys. Lett. 100, 152106 (2012); http://dx.doi.org/10.1063/1.3702577 (3 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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Coincident site lattice-matched wurtzite (0001) In0.31Ga0.69N, emitting in the important green wavelength region, is demonstrated by molecular beam epitaxy on a cubic (111) MgAl2O4 spinel substrate. The coincident site lattice matching condition involves a 30° rotation between the lattice of the InGaN epitaxial layer and the lattice of the spinel. This work describes an alternative approach towards realizing more compositionally homogenous InGaN films with low dislocation density emitting in the “green gap” of low efficiency currently observed for semiconductor light emitting diodes (LEDs). This approach could lead to higher efficiency green LEDs presently of great interest for solid-state lighting applications.
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68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Identification of a paramagnetic recombination center in silicon/silicon-dioxide interface

T. Matsuoka, L. S. Vlasenko, M. P. Vlasenko, T. Sekiguchi, and K. M. Itoh

Appl. Phys. Lett. 100, 152107 (2012); http://dx.doi.org/10.1063/1.3702785 (3 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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A paramagnetic recombination center having an orthorhombic symmetry with g[110] = 2.0095(2), g[001] = 2.0038(2), and g[math10] = 2.0029(2) is found at the interface between silicon and native oxide. The center is referred to Pm center and observed by a spin dependent recombination based electron paramagnetic resonance detection that has the sensitivity of ∼1011 spins/cm2. The employment of an isotopically enriched 28Si sample with the concentration of 29Si nuclear spins reduced to 0.017% leads to narrowing of the resonance line. This narrowing is the key for the accurate determination of the angular dependence of the g-factor.
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75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
76.30.Lh Other ions and impurities
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

Reliability improvement of InGaZnO thin film transistors encapsulated under nitrogen ambient

Chun-Yu Wu, Huang-Chung Cheng, Chao-Lung Wang, Ta-Chuan Liao, Po-Chun Chiu, Chih-Hung Tsai, Chun-Hsiang Fang, and Chung-Chun Lee

Appl. Phys. Lett. 100, 152108 (2012); http://dx.doi.org/10.1063/1.3702794 (4 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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The nitrogen ambient encapsulation (NAE) technique is introduced to improve the reliability issue for the amorphous InGaZnO (a-IGZO) thin-film transistors under positive gate bias stress (PGBS). For the NAE devices, the threshold voltage (Vth) shift is significantly decreased from 1.88 to 0.09 V and the reduction of saturation drain current is improved from 15.75 to 5.61 μA as compared to the bare a-IGZO counterparts after PGBS. These improvements are attributed to the suppression of negatively charged oxygen adsorption on the a-IGZO backsurface and thereby well maintain the channel potential of NAE devices, which in turn sustain the Vth during PGBS.
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85.30.Tv Field effect devices

Spin state transition and giant dielectric constant in Pr0.987Na0.013CoO3

Heng Wang, Guangshe Li, Minglei Zhao, and Liping Li

Appl. Phys. Lett. 100, 152109 (2012); http://dx.doi.org/10.1063/1.3701613 (4 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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Pr0.987Na0.013CoO3 exhibits an anomaly in magnetic susceptibility and transport behavior around 200 K, which is associated with a thermally excited spin transition of Co3+. We show that introduction of Na+ in PrCoO3 induced a variable range hopping (VRH) conduction. At the transition temperature, the density of state near Fermi level increased, while the hopping distance and hopping energy decreased. Extrinsic electrode polarization was also observed at low frequency, leading to a giant dielectric constant. Both conductivity and dielectric relaxation frequency in bulk follow a simple temperature dependence, T−1/4, indicating a close relationship between VRH conduction and dielectric relaxation.
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77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation
72.20.Ee Mobility edges; hopping transport
75.30.Cr Saturation moments and magnetic susceptibilities
75.80.+q Magnetomechanical effects, magnetostriction

Spectra of Rashba- and Dresselhaus-type circular photogalvanic effect at inter-band excitation in GaAs/AlGaAs quantum wells and their behaviors under external strain

J. L. Yu, Y. H. Chen, Y. Liu, C. Y. Jiang, H. Ma, and L. P. Zhu

Appl. Phys. Lett. 100, 152110 (2012); http://dx.doi.org/10.1063/1.3702826 (5 pages) | Cited 2 times

Online Publication Date: 12 April 2012

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Spectra of Rashba- and Dresselhaus-type circular photogalvanic effect (CPGE) at inter-band excitation in symmetric GaAs/Al0.3Ga0.7As quantum wells have been investigated at room temperature. The lineshape of Rashba and Dresselhaus-type CPGE spectra is similar, and the Rashba-type is about five times larger than that of Dresselhaus-type. The CPGE current for 1HH-1E (the first valence subband of heavy hole to the first conduction) has the same sign with that of 1LH-1E, while the strain-induced Rashba-type CPGE has different sign for them, and no detectable strain-induced Dresselhaus-type CPGE is observed.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.35.-y Excitons and related phenomena
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
73.21.Fg Quantum wells

Epitaxial ferromagnetic nanoislands of cubic GdN in hexagonal GaN

T. F. Kent, J. Yang, L. Yang, M. J. Mills, and R. C. Myers

Appl. Phys. Lett. 100, 152111 (2012); http://dx.doi.org/10.1063/1.3702843 (4 pages) | Cited 1 time

Online Publication Date: 12 April 2012

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Periodic structures of GdN particles encapsulated in a single crystalline GaN matrix were prepared by plasma assisted molecular beam epitaxy. High resolution x-ray diffractometery shows that GdN islands, with rock salt structure are epitaxially oriented to the wurtzite GaN matrix. Scanning transmission electron microscopy combined with in situ reflection high energy electron diffraction allows for the study of island formation dynamics, which occurs after 1.2 monolayers of GdN coverage. Magnetometry reveals two ferromagnetic phases, one due to GdN particles with Curie temperature of 70 K and a second, anomalous above room temperature phase.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Suppression of threading defects formation during Sb-assisted metamorphic buffer growth in InAs/InGaAs/InP structure

A. Gocalinska, M. Manganaro, and E. Pelucchi

Appl. Phys. Lett. 100, 152112 (2012); http://dx.doi.org/10.1063/1.3703587 (5 pages) | Cited 2 times

Online Publication Date: 12 April 2012

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A virtual substrate for high quality InAs epitaxial layer has been attained via metalorganic vapor-phase epitaxy growth of Sb-assisted InxGa1−xAs metamorphic buffers, following a convex compositional continuous gradient of the In content from x = 53% to 100%. The use of trimethylantimony (or its decomposition products) as a surfactant has been found to crucially enable the control over the defect formation during the relaxation process. Moreover, an investigation of the wafer offcut-dependence of the defect formation and surface morphology has enabled the achievement of a reliably uniform growth on crystals with offcut towards the [111]B direction.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

High frequency clipper like behavior of tri-layer nickel oxide stack

S. P. Koiry, R. Ratnadurai, S. Krishnan, and S. Bhansali

Appl. Phys. Lett. 100, 152113 (2012); http://dx.doi.org/10.1063/1.3703589 (5 pages)

Online Publication Date: 12 April 2012

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We report on AC propagation in vertically stacked tri-layer nickel oxide (NiO) film with gradient in oxide composition. These studies reveal that the stacked film clips both positive and negative peaks of the AC signals and these clipping characteristics are analogous to a symmetrical clipper. These characteristics are obtained without using any clipper circuit elements like diodes or transistors and DC power source. We propose that the clipping characteristic of NiO stack is a result of space charge generated during signal propagation.
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73.61.Ng Insulators
73.50.Fq High-field and nonlinear effects

Improved photoresponsivity of semiconducting BaSi2 epitaxial films grown on a tunnel junction for thin-film solar cells

Weijie Du, Mitsushi Suzuno, M. Ajmal Khan, Katsuaki Toh, Masakazu Baba, Kotaro Nakamura, Kaoru Toko, Noritaka Usami, and Takashi Suemasu

Appl. Phys. Lett. 100, 152114 (2012); http://dx.doi.org/10.1063/1.3703585 (3 pages) | Cited 9 times

Online Publication Date: 13 April 2012

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The highest photoresponsivity and an internal quantum efficiency exceeding 70% at 1.55 eV were achieved for 400 nm thick undoped n-type BaSi2 epitaxial layers formed on a n+-BaSi2/p+-Si tunnel junction (TJ) on Si(111). The diffusion of Sb atoms was effectively suppressed by an intermediate polycrystalline Si layer grown by solid phase epitaxy, located between the TJ and undoped BaSi2 layers.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.Pa Diffusion in nanoscale solids
73.40.Gk Tunneling

The integration of high-k dielectric on two-dimensional crystals by atomic layer deposition

Han Liu, Kun Xu, Xujie Zhang, and Peide D. Ye

Appl. Phys. Lett. 100, 152115 (2012); http://dx.doi.org/10.1063/1.3703595 (4 pages) | Cited 5 times

Online Publication Date: 13 April 2012

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We investigate the integration of Al2O3 high-k dielectric on two-dimensional (2D) crystals of boron nitride (BN) and molybdenum disulfide (MoS2) by atomic layer deposition (ALD). We demonstrate the feasibility of direct ALD growth with trimethylaluminum and water as precursors on both 2D crystals. Through theoretical and experimental studies, we found that the initial ALD cycles play the critical role, during which physical adsorption dominates precursor adsorption at the crystal surface. We model the initial ALD growth stages at the 2D surface by analyzing Lennard-Jones potentials, which could guide future optimization of the ALD process on 2D crystals.
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77.55.D- High-permittivity gate dielectric films
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Role of surface trap states on two-dimensional electron gas density in InAlN/AlN/GaN heterostructures

S. Pandey, D. Cavalcoli, B. Fraboni, A. Cavallini, T. Brazzini, and F. Calle

Appl. Phys. Lett. 100, 152116 (2012); http://dx.doi.org/10.1063/1.4703938 (4 pages) | Cited 6 times

Online Publication Date: 13 April 2012

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In order to clarify the effect of charged dislocations and surface donor states on the transport mechanisms in polar AlInN/AlN/GaN heterostructures, we have studied the current-voltage characteristics of Schottky junctions fabricated on AlInN/AlN/GaN heterostructures. The reverse-bias leakage current behaviour has been interpreted with a Poole-Frenkel emission of electrons from trap states near the metal-semiconductor junction to dislocation induced states. The variation of the Schottky barrier height as a function of the AlN layer thickness has been measured and discussed, considering the role of the surface states in the formation of the two dimensional electron gas at AlN/GaN interface.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
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